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+;;; test-custom-whitespace-hyphenate.el --- Tests for cj/--hyphenate-whitespace -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the cj/--hyphenate-whitespace function from custom-whitespace.el
+;;
+;; This function replaces all runs of whitespace (spaces, tabs, newlines,
+;; carriage returns) with single hyphens. Useful for converting text with
+;; whitespace into hyphenated identifiers or URLs.
+;;
+;; Uses the regexp [ \t\n\r]+ to match whitespace runs.
+;;
+;; We test the NON-INTERACTIVE implementation (cj/--hyphenate-whitespace)
+;; to avoid mocking region selection. This follows our testing best practice
+;; of separating business logic from UI interaction.
+
+;;; Code:
+
+(require 'ert)
+(require 'testutil-general)
+
+;; Add modules directory to load path
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+;; Stub dependencies before loading the module
+(defvar cj/custom-keymap (make-sparse-keymap)
+  "Stub keymap for testing.")
+
+;; Now load the actual production module
+(require 'custom-whitespace)
+
+;;; Test Helpers
+
+(defun test-hyphenate-whitespace (input-text)
+  "Test cj/--hyphenate-whitespace on INPUT-TEXT.
+Returns the buffer string after operation."
+  (with-temp-buffer
+    (insert input-text)
+    (cj/--hyphenate-whitespace (point-min) (point-max))
+    (buffer-string)))
+
+;;; Normal Cases
+
+(ert-deftest test-hyphenate-whitespace-single-space ()
+  "Should replace single space with hyphen."
+  (let ((result (test-hyphenate-whitespace "hello world")))
+    (should (string= result "hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-multiple-spaces ()
+  "Should replace multiple spaces with single hyphen."
+  (let ((result (test-hyphenate-whitespace "hello    world")))
+    (should (string= result "hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-tabs ()
+  "Should replace tabs with hyphen."
+  (let ((result (test-hyphenate-whitespace "hello\tworld")))
+    (should (string= result "hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-mixed-tabs-spaces ()
+  "Should replace mixed tabs and spaces with single hyphen."
+  (let ((result (test-hyphenate-whitespace "hello \t world")))
+    (should (string= result "hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-newlines ()
+  "Should replace newlines with hyphen (joining lines)."
+  (let ((result (test-hyphenate-whitespace "hello\nworld")))
+    (should (string= result "hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-multiple-newlines ()
+  "Should replace multiple newlines with single hyphen."
+  (let ((result (test-hyphenate-whitespace "hello\n\n\nworld")))
+    (should (string= result "hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-multiple-words ()
+  "Should hyphenate multiple words with various whitespace."
+  (let ((result (test-hyphenate-whitespace "one two  three\tfour\nfive")))
+    (should (string= result "one-two-three-four-five"))))
+
+(ert-deftest test-hyphenate-whitespace-carriage-returns ()
+  "Should handle carriage returns."
+  (let ((result (test-hyphenate-whitespace "hello\r\nworld")))
+    (should (string= result "hello-world"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-hyphenate-whitespace-empty-string ()
+  "Should handle empty string."
+  (let ((result (test-hyphenate-whitespace "")))
+    (should (string= result ""))))
+
+(ert-deftest test-hyphenate-whitespace-no-whitespace ()
+  "Should handle text with no whitespace (no-op)."
+  (let ((result (test-hyphenate-whitespace "helloworld")))
+    (should (string= result "helloworld"))))
+
+(ert-deftest test-hyphenate-whitespace-only-whitespace ()
+  "Should convert text with only whitespace to single hyphen."
+  (let ((result (test-hyphenate-whitespace "   \t   \n   ")))
+    (should (string= result "-"))))
+
+(ert-deftest test-hyphenate-whitespace-single-char ()
+  "Should handle single character with surrounding spaces."
+  (let ((result (test-hyphenate-whitespace "  x  ")))
+    (should (string= result "-x-"))))
+
+(ert-deftest test-hyphenate-whitespace-very-long-text ()
+  "Should handle very long text with many spaces."
+  (let ((result (test-hyphenate-whitespace "word word word word word word word word")))
+    (should (string= result "word-word-word-word-word-word-word-word"))))
+
+(ert-deftest test-hyphenate-whitespace-leading-whitespace ()
+  "Should replace leading whitespace with hyphen."
+  (let ((result (test-hyphenate-whitespace "   hello world")))
+    (should (string= result "-hello-world"))))
+
+(ert-deftest test-hyphenate-whitespace-trailing-whitespace ()
+  "Should replace trailing whitespace with hyphen."
+  (let ((result (test-hyphenate-whitespace "hello world   ")))
+    (should (string= result "hello-world-"))))
+
+;;; Error Cases
+
+(ert-deftest test-hyphenate-whitespace-start-greater-than-end ()
+  "Should error when start > end."
+  (should-error
+   (with-temp-buffer
+     (insert "hello world")
+     (cj/--hyphenate-whitespace (point-max) (point-min)))
+   :type 'error))
+
+(ert-deftest test-hyphenate-whitespace-empty-region ()
+  "Should handle empty region (start == end) without error."
+  (with-temp-buffer
+    (insert "hello world")
+    (let ((pos (/ (+ (point-min) (point-max)) 2)))
+      (cj/--hyphenate-whitespace pos pos)
+      ;; Should complete without error and not change buffer
+      (should (string= (buffer-string) "hello world")))))
+
+(provide 'test-custom-whitespace-hyphenate)
+;;; test-custom-whitespace-hyphenate.el ends here